Identifying subjects who are likely to develop high levels of dental caries based on results from simple salivary assays for microorganism counts was the focal point of this study. It is known that these microorganism assays are of limited value in areas with low caries prevalence. Therefore, we studied an adolescent Icelandic population whose mean DMFS scores were roughly 3 times that of their US counterparts. The basic findings were that the microorganism assays were also of limited value in a high caries prevalence population, although their positive predictive values were slightly higher than those typically reported in a low caries prevalence population. They also proved not to be significantly better than using the initial DMFS scores for individual subjects, suggesting that they were of no cost-benefit value in targeting subjects at high risk for caries.